What Buck learns from the man in the red sweater is that the man with the club has to be obeyed. In other words, you have to do what the people with the power want you to do.

You can say that this applies to people today as it always has. Might, in some ways, makes right. We may not like it and it may not seem civilized, but at times we simply have to give in to the people with more power. If we are like Buck we can wait and get stronger ourselves and then be the ones with the power. But until we do, we have to obey.

This is partly an admission that we are weaker than someone. But Buck is also smarter than some dogs that fight to the death. Part of what he is saying is that we have to be smart enough to fight when we have a chance to win and to let it go when we don't.